Milil first appeared within Dungeons & Dragons as one of the deities featured in Ed Greenwood's article "Down-to-earth Divinity" in Dragon #54 (October 1981). Milil was introduced as the god of poetry, eloquence, and song, a neutral good demigod from the Happy Hunting Grounds. The article notes that Milil is connected to Oghma and Sune, and states that he is "held in special esteem by bards. He is seen as a young, charismatic man with beautiful features and voice, but is usually manifested as a haunting music (particularly in clearings in the depths of a wood), or a radiance about some human bard or raconteur in the throes of inspiration." Milil's alliances are also described: "Oghma is served by Gond on one hand, and by Milil and Deneir on the other. Milil often works directly with Lliira." Milil is commonly worshipped by neutral good thieves and clerics, as well as any bards, and characters employed as poets, artists, scribes, and sages.
Milil later officially appeared as one of the major deities for the Forgotten Realmscampaign setting, in the Forgotten Realms Campaign Set's "Cyclopedia of the Realms" booklet (1987).